1. Field of the Invention
The present invention relates to a semiconductor device using a transistor including an oxide semiconductor and a method for driving the transistor.
2. Description of the Related Art
Although transistors including amorphous silicon have been used for conventional display devices typified by liquid crystal televisions, an oxide semiconductor has attracted attention as a material which replaces a silicon semiconductor in order to form transistors. For example, an active matrix display device, in which an amorphous oxide including In, Ga, and Zn is used for an active layer of a transistor and the electron carrier concentration of the amorphous oxide is lower than 1018/cm3, is disclosed (see Patent Document 1).
However, some problems of a transistor including an oxide semiconductor have been pointed out. One of the problems is the stability of the characteristics, and it is pointed out that the electric characteristics of the transistor are varied by irradiation with visible light and ultraviolet light.